Mild Cognitive Impairment – An Added Value to Patient and Physician

Dr Henderson is in private practice in Denver, Colorado. He is a board member of the Brain Imaging Council of the Society of Nuclear Medicine and President of The Synaptic Space, a neuroimaging consulting firm, in Centennial, Colorado.

The recent commentary by Dr Ronald Pies concerning the changes in the diagnostic criteria for Alzheimer’s disease (AD) and Mild Cognitive Impairment (MCI), questioned the value of informing a patient early in the course of a dementing illness……

While there are currently no treatments for AD, it is important to examine what we are treating. By the time AD is diagnosed by clinical symptoms, 8 to possibly 15 years of pathological damage has already occurred. Just as in Parkinson’s disease wherein over 80% of the substantia nigra neurons must be lost before symptoms manifest, the AD-related damage to the entorhinal cortex, hippocampus, and parietal cortex are much advanced by the time a drop in the Mini-Mental-Status Examination score occurs. Treatment at this point cannot undo the pathological damage. Therapeutic interventions, to be effective, must be introduced as early as possible in the pathological process.

Perfusion SPECT neuroimaging can identify MCI with an accuracy of as high as 99%.2-5 Amyloid markers can differentiate AD from controls with 85% to 95% sensitivity and 91% to 100% specificity in advanced cases.6-9 But these markers can also identify MCI with 80 % sensitivity and 90% specificity10; however, it must be noted that 10% of controls aged 50 years have a positive amyloid scan. This false positive rate increases by 10% each decade.6 Nonetheless, neuroimaging provides an endophenotype which can be quantified and detected long before the patient begins to show the cognitive dysfunction of AD or MCI. The implications are tremendous, not just in terms of early intervention, but also in terms of speeding clinical trials. Currently, we must wait years to see if a therapeutic intervention is making a difference……